1. Field of the Invention
The present invention relates to a trigger circuit for an electromagnetic actuator, comprising an energy storage located in the vicinity of the actuator, said energy storage being connected with a remotely arranged supply source via supply lines, at least one electronic switch defining, together with the actuator, a first series circuit, and a sensor responding to danger situations.
2. Description of Related Art
Trigger circuits for electromagnetic actuators are frequently used in the vicinity of potentially explosive areas, for example in the chemical industry. Typical electromagnetic actuators are actuators for valves, e.g. linear actuators for shutoff valves. In protective systems, these valves serve for very rapidly switching on or off mass and volume flows, or for very rapidly pre-controlling suitable shutoff devices and thus performing switching actions. The operation of electromagnetic actuators requires a very high power to be provided for a short time. If the energy required for the switching action must be transmitted through the potentially explosive area, the power involved must be transmitted in an explosion-protected manner.
For preventing high currents from flowing through the supply lines, it is common practice to arrange an energy storage in the vicinity of the electronic switch and, if the sensors responds, to discharge the energy storage via the series circuit defined by the then closed electronic switch and the actuator.
One aspect of the present invention is based on a trigger circuit of EP 1 498 912 A1 of the applicant company. The trigger circuit described here comprises two electronic switches connected in series with the actuator in the form of triacs. The triacs are controlled via optocouplers. The trigger command for operating the actuator has the effect that a polarity inversion of the supply voltage takes place, which is transmitted to the optocoupler. The known trigger circuit is expensive on the one hand, and susceptible to malfunction on the other hand, in particular since light emitting diodes and light-sensitive transistors may fail.